Add menu item to delete all beatmap sets in filter groups

[LBlend]

As requested in #36825, this adds a menu item to delete all beatmap sets in whichever group you right click. It will make it easier to mass delete maps and save some precious storage. Considering the spike in SSD prices recently, I for one would like more options to mass delete maps.

Things that should maybe be addressed, hence why this is a draft:

• When grouping by last played, if a subset of difficulties appear and you hit delete, it will delete the whole map set, which might be unexpected for some people. Though, this also happens when you hit delete on the difficulty itself so it doesn't diverge from how things are currently done
• Write tests?

[peppy]

This dialog should definitely show a count of how many beatmap sets are to be deleted.

[LBlend]

Good idea! Are you thinking something like this?

[peppy]

I was skeptical that this would be correct for BPM grouping, but it seems we changed that to group by sets therefore it works as expected.

Before merging we want to be 100% sure that this option won't appear on a group which could have partial contents of beatmap sets in it (but cause a deletion of the full sets).

[LBlend]

Before merging we want to be 100% sure that this option won't appear on a group which could have partial contents of beatmap sets in it (but cause a deletion of the full sets).

AFAIK this applies to:

• Last Played
• Collections
• Rank Achieved
• Difficulty ("Fixed". The menu item does not appear for this one)

This is assuming that we're not handling "edge cases", i.e. maps that have difficulties with different songs, which will have different BPMs, titles, artists, sources etc.

I'll look into it!

[peppy]

This is assuming that we're not handling "edge cases", i.e. maps that have difficulties with different songs, which will have different BPMs, titles, artists, sources etc.

Based on our current grouping rules, this is not feasible technically. So I think we're fine. But it needs confirmation/safeties at a code level to ensure we don't shoot ourselves in the foot.